| Abstract |
The high cost of re-injection of geothermal discharge waters is largely due to their silica deposition potential. of Wairakei discharge waters is really necessary to solve any environmental problems due to arsenic, hron, lithium, mercury or waste heat. One should ask if reinjection Alternative strategies are: 1. Doing nothing, and continuing discharging the geothermal waters from Wairakei into the Waikato River. . 2. Chemical treatment to 'remove arsenic together with prevention of silica scaling and removal of waste heat. A successful pilot plant will be de'scribed which achieves these aims by a method particularly suitable to Wairakei waters. ' Alas-boron and lithium remain. 3. A more controversial suggestion involves chemical treatment of Wairakei waters as in No. 2, which might then allow direct disch;.:rge from a second geothermal station into the Waikato River without exceeding the WHO (World Health Authority) arsenic limit for drinking water. . The economics and our present' state of knowledge of the environmental consequences of these options will be discussed. It is believed that present or projected levels of boron and lithium in the Waikato are unlikely to cause any harmful effects; however, more work is required to allow the public to be convinced of this. Nearly all of the mercury evolved is in the geothermal steam, and therefore neither treatment nor reinjection of discharge waters will have any effect on the mercury level of the Waikato River. In other geothermal stations (e-g. Ohaaki and Mokai) partial removal of silica, by a method being tested on pilot plants by Industrial Processing Division and Chemistry Division, would allow reinjection to be carried out at lower temperatures. |